Non-contact actuation of triple-shape effect in multiphase polymer network nanocomposites in alternating magnetic field

Abstract

Triple-shape polymers (TSP) can memorize two independent shapes, which are recovered when the temperature is subsequently increased. Certain applications do not allow triggering of the triple-shape effect (TSE) by environmental heating (e.g. potential damaging of surrounding tissue) and therefore require a non-contact activation. Here we explored whether polymer nanocomposites can be designed, which enable non-contact activation of TSE in an alternating magnetic field. A series of nanocomposites were synthesized by incorporation of silica coated iron(III)oxide nanoparticles into a polymer network matrix containing poly(e-caprolactone) (PCL) and poly(cyclohexyl methacrylate) (PCHMA) segments. Triple-shape functionalization of the materials was realized by application of different thermomechanical procedures (single or two dual-step), in which samples were deformed by bending to minimize changes in S/V ratio during shape recovery. For quantification of triple-shape properties inductive heating experiments were conducted in an alternating magnetic field at frequency of f = 258 kHz. By increasing the magnetic field strength H the triple-shape effect was triggered, while the maximum achievable temperature Tmax and the shape change was monitored using an infrared video camera. Excellent triple-shape properties were achieved for nanocomposites containing 40 wt-% of PCL exhibiting a two-step recovery of shapes B and C, when stimulated by step-wise increasing the magnetic field strength. In this way the TSE could be characterized by two distinct switching magnetic strengths Hsw,1(A → B) and Hsw,2(B → C) corresponding to the switching temperatures determined in cyclic, thermomechanical tensile tests for thermally-induced TSP.